In a typical electric arc furnace or other steel making furnace, several thousand tonnes of flue dust are generated each year. The constitution of the flue dust varies with the feed material to the furnace which normally consists of or includes a wide range of scrap metal including old motor cars. The flue dust may contain about 40% of non-ferrous metallic compounds, about 50% ferrous compounds (mainly oxide) with the remainder being gangue material. The non-ferrous metallic constituents are normally predominantly lead oxide and zinc oxide but typically include some zinc chloride, copper chloride, cadmium chloride, potassium chloride, sodium chloride and cadmium oxide. Oxides of potassium and sodium may also be present. Flue dust from a basic oxygen furnace normally contains a higher proportion of ferrous compounds but there are still significant proportions of non-ferrous material.
Historically, flue dust has been dumped but this involves a substantial cash expenditure and is becoming environmentally less acceptable due to the toxicity of many of the constituents. The invention is concerned particularly with a process for reclaiming constituents from a material such as flue dust. The invention may be looked on primarily as a means for avoiding disposal of contaminants or as a means of extracting valuable non-ferrous metals or as a means of recuperating iron for re-use in the steel making process. The dominant objective depends on the circumstances.
It is already known from EP 275863A to mix flue dust with solid carbonaceous material and an organic binder, pelletize this mixture and heat the pellets. Some constituents are driven off while iron and lead are reduced to the metallic form and poured off as liquid metal. It is stated that the lead can be separated from the iron gravitationally but some lead must remain in solution in the iron. Also, very high temperatures have to be used to achieve the molten state for the iron and extracting the metal in molten form requires a facility such as tilting a rotary kiln and is not convenient for continuous operation.